An Overseer Music Box.
Overseer Music Boxes is an audiograph found in Dishonored, recorded by an unidentified Overseer.
Transcript[]
We cannot doubt the effectiveness of Holger's Device, or the mathematical beauty of the music itself; we've seen it in action against the forbidden practices too many times to deny it. But the question no one wishes to ask is - is the incantation itself black magic? The boxes are priceless, but what's inside?
Location[]
The audiograph can be found during the mission High Overseer Campbell, in the locked workshop in the Back Yard.